I was reminded not too long ago that not all Mac Users understand the trash can. Not just the main Trash located on their Dock but Trash in applications like iPhoto and Mail. Not only do you have to throw away the files you don’t want but you also have to tell the Trash to empty after you move the files there. If you do not empty the Trash the files stay on your hard drive and sometimes manage to fill it up to the point of  corruption. So empty the Trash often. For those of you who put items in the Trash and use it as a holding bin: DON’T. Never put anything in there that you want to keep. If you feel the need to archive some files burn them to a CD or move them to a external hard drive, then throw them away and empty the Trash. If your Trash tells you that it can’t throw away certain files try again holding down the Option key as you empty the Trash. I have even had times I needed to "secure empty trash" before items would allow themselves to be removed.